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P A R T 7
Drugs acting on the reproductive system
The external genitalia—the clitoris, labia and vagina—
are sites of erogenous stimulation and the entry way for
sperm to reach the uterus to allow conception and the
exit path for the developed fetus at birth. Development
of the breast tissue, also considered a secondary sex char-
acteristic, is controlled by the female sex hormones and
is necessary for producing milk for the nourishment of
the baby when it has been expelled from the uterus and
is no longer able to be dependent on the mother’s blood
supply for nourishment.
Hormones
The hormones produced in the ovaries are oestrogen
and progesterone. These two hormones influence many
other body systems while preparing the body for preg-
nancy or maintenance of pregnancy.
Oestrogen
The oestrogens produced by the ovaries include oestrad
iol, oestrone and oestriol. The oestrogens enter cells
and bind to receptors within the cytoplasm to promote
messenger RNA (mRNA) activity, which results in pro-
duction of specific proteins for cell activity or structure.
Many of these effects are first noticed at menarche
(the onset of the menstrual cycle), when the hormones
begin cycling for the first time. Female characteristics
are associated with the effects of oestrogen on many of
the body’s systems—wider hips, soft skin, breast growth
and so on. Box 39.1 summarises the effects of oestrogen
on the body.
Progesterone
Progesterone is released into circulation after ovulation.
Progesterone has many effects that support the early
development of the fetus. Progesterone’s effects on body
temperature are monitored in the “rhythm method” of
birth control to indicate that ovulation has just occurred.
Box 39.2 summarises the effects of progesterone on the
body.
Control mechanisms
The developing hypothalamus is sensitive to the andro-
gens released by the adrenal glands and does not release
GnRH during childhood. As the hypothalamus matures,
it loses its sensitivity to the androgens and starts to
release GnRH. This occurs at
puberty
, or sexual
development. The onset of puberty leads to a number of
hormonal changes. See Figure 39.2.
GnRH stimulates the anterior pituitary to release
FSH and LH. FSH and LH stimulate the follicles on the
outer surface of the ovaries to grow and develop. These
follicles, called Graafian follicles, produce progesterone,
which is retained in the follicle, and oestrogen, which is
released into circulation. When the circulating oestrogen
level rises high enough, it stimulates a massive release of
LH from the anterior pituitary. This is called the “LH
surge”. This burst of LH causes one of the developing
follicles to burst and release the ovum with its stored
hormones into the system. LH also causes the rest of
the developing follicles to shrink in on themselves, or
involute and eventually disappear. The release of an
ovum from the follicle is called
ovulation
.
The ovum is released into the abdomen near the end
of one of the fallopian tubes, and the constant movement
of cilia within the tube helps to propel the ovum into
Growth of genitalia (in preparation for childbirth)
Growth of breast tissue (in preparation for pregnancy
and breastfeeding)
Characteristic female pubic hair distribution (a triangle)
Stimulation of protein building (important for the
developing fetus)
Increased total blood cholesterol (for energy for the
mother as well as the developing fetus) with an
increase in high-density lipoprotein levels (“good”
cholesterol, which serves to protect the female blood
vessels against atherosclerosis)
Retention of sodium and water (to provide cooling for
the heat generated by the developing fetus and to
increase diffusion of sodium and water to the fetus
through the placenta)
Inhibition of calcium resorption from the bones (helps to
deposit calcium in the fetal bone structure; when this
property is lost at menopause, osteoporosis, or loss of
calcium from the bone, is common)
Alteration of pelvic bone structure to a wider and flaring
pelvis (to promote easier delivery)
Closure of the epiphyses (to conserve energy for the fetus
by halting growth of the mother)
Increased thyroid hormone globulin (metabolism needs
to be increased greatly during pregnancy, and the
increase in thyroid hormone facilitates this)
Increased elastic tissue of the skin (to allow for the
tremendous stretch of the abdominal skin during
pregnancy)
Increased vascularity of the skin (to allow for radiation
loss of heat generated by the developing fetus)
Increased uterine motility (oestrogen is high when the
ovum first leaves the ovary, and increased uterine
motility helps to move the ovum towards the uterus
and to propel the sperm towards the ovum)
Thin, clear cervical mucus (allows easy penetration of
the sperm into the uterus as ovulation occurs; used in
fertility programs as an indication that ovulation will
soon occur)
Proliferative endometrium (to prepare the lining of the
uterus for implantation with the fertilised egg)
Anti-insulin effect with increased glucose levels (to allow
increased diffusion of glucose to the developing fetus)
T-cell inhibition (to protect the non-self cells of the
embryo from the immune surveillance of the mother)
■■
BOX 39.1
Effects of oestrogen
